1. Field of the Invention
The present invention relates to an automatic control method and an automatic control system for optimum mixing of raw materials for cement.
2. Description of the Related Art
A raw material mixing control system of a cement production plant has a structure, for example, as shown in FIG. 4. In FIG. 4, the reference numerals 1, 2 represent holding hoppers for holding different kinds of raw materials for cement. As shown in FIG. 4, raw materials for cement are taken out of the holding hoppers 1, 2, in predetermined amounts at a time, by feed wares 3, 4, mixed together, and guided by a belt conveyor 5 to a raw material pulverizing mill 6, where they are pulverized.
The raw materials pulverized by the raw material pulverizing mill 6 are guided to a separator 8 via a bucket elevator 7. In the separator 8, the raw material mixture is classified, and the resulting coarse powder is sent again to the raw material pulverizing mill 6. The raw material mixture deprived of the coarse powder is guided to a blending silo (not shown) via a component analyzer 9.
Data on the proportions of the constituents (CaO, SiO.sub.2, Al.sub.2 O.sub.3, Fe.sub.2 O.sub.3) of the raw material mixture fed to the component analyzer 9 are supplied to a computer 10. The computer 10 records the takeout amounts of the respective raw materials that have been detected with takeout amount detectors 11, 12 provided in the feed wares 3, 4.
A functional block diagram of conventional control of mixing is given as FIG. 5.
In FIG. 5, deviations are calculated between targeted modulus values 13 of modulus parameters, and their measured modulus values 15 calculated from the measurements made by the component analyzer 9. The modulus parameters include a hydraulic modulus HM, a silica modulus SM, and an iron modulus IM. These moduli are defined as follows: EQU HM=(CaO)/(SiO.sub.2 +Al.sub.2 O.sub.3 +Fe.sub.2 O.sub.3) (1) EQU SM=(SiO.sub.2)/(Al.sub.2 O.sub.3 +Fe.sub.2 O.sub.3) (2) EQU IM=(Al.sub.2 O.sub.3)/(Fe.sub.2 O.sub.3) (3)
When the above deviations amount to certain values or more, estimates of the component contents of raw materials, to be used in the calculation of a mixture ratio, are made, as designated by 16, on the basis of measured component contents 19 of raw materials for calculation of a mixture ratio. In view of the results, the raw material component contents to be used in calculation of a mixture ratio are updated.
Raw material component content estimated values 20 obtained by these calculations, and deviations 21 between the measured values and the target values of the above-described modulus parameters are used to solve simultaneous equations 17 composed of the equations for the proportions of components (the equations defining the modulus parameters), and equations for material balances. The takeout amounts of the raw materials for bringing the measured values of the modulus parameters into agreement with their target values are calculated thereby. This outcome is put out to the feed wares 3, 4.
Earlier technologies posed the following problems: First, the estimated values 20 of the components of raw materials to be mixed can deviate from the actual values, resulting in the wrong calculated takeout amounts. Secondly, if the measurements of the mixed raw materials made by the component analyzer vary greatly, the simultaneous equations 17 including the equations for the proportions of components, and the equations for material balances may fail to give a solution which satisfies the capacities of the feed wares 3, 4. Among such cases is the possibility that the estimated values 20 of the contents of the components of the raw materials will be negative.
If the number of the raw materials coincides with the number of the simultaneous equations, a solution usually exists. Especially when variations in the chemical compositions of the raw materials are small, the solutions to the simultaneous equations become solutions falling within the scope of the capacities of the feed wares.
When variations in the chemical compositions of the raw materials are large, namely, when the component of some of the raw materials greatly varies, however, the solutions to the simultaneous equations fail to lie within the scope of the capacities of the feed wares. Even in this case, control of raw material mixing should not be discontinued. Thus, in such a case, mixing of the raw materials has been performed by activating an alarm by the computer, switching the setting of the raw material supply amounts from an automatic mode to a manual mode, and relying on a human judgment thereafter. Such control of mixing by human judgment generally creates the problem that differences from an individual to another individual show up markedly.
If the number of the supplied raw materials is greater or smaller than the number of the simultaneous equations, solutions to the simultaneous equations maybe infinite in number or none. Under this situation, no methods are established for solving the simultaneous equations, so that there is no choice other than to rely on a manual operation. Even if the control is performed using the computer, the only feasible manner of control has been such that the hydraulic modulus HM alone is controlled, without simultaneous consideration of all three modulus parameters (HM, silica modulus SM, and iron modulus IM).